Machines such as on- or off-highway haul trucks, motor graders, snow plows, and other types of heavy equipment are used to perform a variety of tasks. Some of these tasks involve carrying or pushing large, awkward, loose, and/or heavy loads up steep inclines or along rough or poorly marked haul roads. And, because of the size and momentum of the machines and/or because of poor visibility, these tasks can be difficult for a human operator alone to complete effectively.
To help guide large machines safely and efficiently along haul roads, some machines are equipped with sensors, for example, GPS sensors, RADAR sensors, SONAR sensors, LIDAR sensors, IR and non-IR cameras, and other similar sensors. These sensors are often connected to a visual display and/or to a guidance system of the machine such that control over machine maneuvering may be enhanced or even automated. In order for these display and guidance systems to operate properly, the information provided by the sensors must be accurate. And, even though most machine sensor systems are calibrated when first commissioned, vibrations, collisions, and damage to the machine during operation can reduce the quality of information provided by the sensors. As such, periodic checks on the integrity of the sensors can be beneficial.
An exemplary machine system that provides periodic integrity checks is disclosed in U.S. Pat. No. 5,906,655 issued to Fan on May 25, 1999 (“the '655 patent”). Specifically, the '655 patent discloses an integrated machine positioning system having a GPS receiver and an Inertial Navigation Unit (INU). The INU includes an odometer, a Doppler radar, a gyroscope, and a sensor for measuring a steering angle of a mobile machine. The machine positioning system receives a GPS position estimate from the GPS receiver and an INU position estimate from the INU, and compares the two position estimates. If the two position estimates are the same, the system is considered valid. Otherwise, the velocity of the mobile machine, as determined by the odometer and by the Doppler radar, are compared. If the difference in velocities is greater than a first predetermined threshold, then the INU is determined to be invalid. If the difference in velocities is less than the first predetermined threshold, a heading rate from the gyroscope is compared with a calculated heading rate based on measured steering angle and velocity. If the difference in heading rates is greater than a second predetermined threshold, then the INU is considered to be invalid. Otherwise, the GPS is considered to be invalid.
Although the machine positioning system of the '655 patent may be helpful in some situations, the system may be less than optimal. Specifically, the system requires two separate and redundant navigation units, which can increase the cost and complexity of the system. In addition, the system may be prone to false alarms due to transient changes in sensor values, sensor noise, and external conditions such as machine slipping and sliding. Further, the system of the '655 patent may be unable to detect error drift over time.
The disclosed navigation system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.